Medical device with fail-safe power supply

Abstract

A medical device with a power supply for connecting to an AC power grid in the range of >50 VAC to 264 VAC (wide range) features a circuit for only connecting at least one discharge resistor in parallel to at least one smoothing capacitor if no AC input voltage is present at the power supply. The power supply features a rectifier and at least one smoothing capacitor for smoothing a direct voltage to be supplied by the power supply, as well as at least one discharge resistor for discharging the smoothing capacitor. The power supply features a circuit electrically connected to the discharge resistor and the smoothing capacitor, designed to detect a switched-on state of the medical device with an AC input voltage present at its power supply, and to only connect the discharge resistor in parallel to the smoothing capacitor if the circuit does not detect a switched-on state.

The invention claimed is: 
     
       1. A medical device comprising:
 a power supply for connecting to an AC power grid, the power supply having:
 a bridge rectifier; 
 a smoothing capacitor for smoothing a DC voltage to be supplied by the power supply; 
 a discharge resistor for discharging the smoothing capacitor; and 
 a circuit that is electrically connected to the discharge resistor and the smoothing capacitor and configured to detect a switched-on state of the medical device, with an AC input voltage present at its power supply, across an entire input voltage range, and to only connect the discharge resistor in parallel to the smoothing capacitor if the circuit does not detect a switched-on state of the medical device, the circuit having:
 a first transistor for connecting the discharge resistor in parallel to the smoothing capacitor that is arranged and dimensioned to connect and cause the smoothing capacitor to discharge if a control capacitor connected to a base or a gate of the first transistor is sufficiently charged, the control capacitor being connected to a control transistor that is arranged and dimensioned to regularly connect and discharge the control capacitor as long as the power supply receives a mains voltage; 
 a first resistor; 
 a second resistor; and 
 a circuit capacitor, the first resistor, the second resistor, and the circuit capacitor being connected in series between an input of the bridge rectifier and a negative output of the bridge rectifier, a junction between the second resistor and the circuit capacitor being connected to a base of the control transistor. 
 
 
 
     
     
       2. The medical device according to  claim 1 , wherein the first transistor is a field effect transistor. 
     
     
       3. The medical device according to  claim 2 , further comprising:
 a second capacitor connected in parallel to a gate-drain path of the field effect transistor, the second capacitor, when charged, causing the field effect transistor to connect so that the discharge resistor is connected in parallel to the smoothing capacitor. 
 
     
     
       4. The medical device according to  claim 1 , wherein the circuit is configured to pick up a voltage between a connection on an input side of the bridge rectifier and a connection on an output side of the bridge rectifier and to detect a presence of the mains voltage present at the connection on the input side of the bridge rectifier. 
     
     
       5. The medical device according to  claim 4 , wherein the circuit has a voltage divider comprised of the first resistor, the second resistor, and the circuit capacitor, and a first capacitor that is connected in parallel to the second resistor and charged to a voltage defined by the voltage divider if the mains voltage is present. 
     
     
       6. The medical device according to  claim 1 , wherein a base-emitter path of the control transistor is connected in parallel to the second resistor, and the control transistor connects if the mains voltage is present in a range of >50 V AC  . . . 264 V AC  is present. 
     
     
       7. The medical device according to  claim 1 , wherein the control transistor is a bipolar transistor. 
     
     
       8. The medical device according to  claim 7 , wherein the second capacitor is connected in parallel to a collector-emitter path of the control transistor so that the second capacitor is discharged when the control transistor is connected, so that the discharge resistor is disconnected from the smoothing capacitor if the mains voltage is present at the input of the bridge rectifier. 
     
     
       9. The medical device according to  claim 1 , wherein the circuit has a Zener diode for voltage limitation. 
     
     
       10. The medical device according to  claim 1 , further comprising several of the discharge resistors connected in parallel. 
     
     
       11. The medical device according to  claim 1 , wherein the discharge resistor has a resistance value between 47 kΩ and 120 kΩ.